Fabricating a Wiring Harness

Alright, you've got this far and you actually want to make your own wiring harness.  It's not hard, it just takes patience.  If you aren't already skilled at soldering and crimping, you will be by the end of this.  There's no place for twisting and taping in a dirt bike wiring harness.

What we will cover on this page is how to actually make the connections: tips on how to join the wires and what to look out for.

First thing, you must plan ahead.  Create or borrow a wiring diagram, like I have on my dual sport page.  You have to know where everything is going before you start.  Then you have to decide the routing you will use so you can figure out how long the wire needs to be.  I used a 7-conductor wire as the backbone of my wiring harness.  You can use individual wires but make sure they are well protected so they don't get chafed.  Once you figure out how long the basic harness needs to be, cut it about 2 feet longer than that.  That will give you a foot on each end to work with.

Starting
The way to do it is to start at the front and work your way to the back, all the time trying to position the wires so that you can use shrink wrap.  The only tape will be on the final outer coating at the cruxes (the places where the harness splits to go to the components.)  You want to cut the wires just long enough to do the job but not too short.  You are trying to minimize the amount of wires so they will all fit under the headlight shroud and under the seat.

Butt Splices
Lets look at the basic butt splice.  The butt splice will allow you to make precise cuts-to-length.

Start with two wires coming from opposite directions

Cut them at the same place.

Now they are the correct length for the job

Strip both ends about 1/4 inch

Don't forget the heat shrink

Solder the joint using a butt splice

Heat the wrap to button it up

See, that was easy.  You will do a lot of these making the harness.  Just be sure to stagger the position of the butt splices.  In other words, don't make all the initial cuts like in the second picture at the exact same location on every set of wires.  That would create a large bulge in the wiring harness at that point.  Stagger them a little so you only have one or two butt splices at any given point in the harness.

Junctions: Joins and Splits
Ok, now we're going to get fancy using something called a ferrule.  A ferrule is a little split cylinder of metal that you crimp over two or more wires to join them together.  This allows you to make neat clean wire junctions to make one wire split into two or join two into one.  Here's the basic technique:

Start with 2 wires

Strip one using a sharp razor blade (careful!)

Slide a ferrule over the wires and crimp

Solder for extra security

Heat shrink over the join/split

Now you have a split or join

These are very useful in tying in components to common hot or ground wires.  In this example, if the white wire was a common switched hot wire, you can tie in each component along the white using the same technique all along the wire.  This type of connection make the harness much less bulky than if you try to join them all together at one point.

Zipping it all up
The reason you start at one end and work your way down is so you always have an end to slide the heat shrink tubing from. It's kind of like one of those childhood games where you have to slide tiles around and only have one free space to move in. Always have a place to slide the heat shrink tubing to while you are soldering so it doesn't shrink prematurely.   Also, I like to reinforce the large split points (for example, where all the wires split off to go the the turn signals, horn and lights) with zip ties.  This helps keep everything together and strengthens it.  After you do all that, make a final wrap with electrical tape to protect the few exposed wires at the junctions.